A Lundell rotor includes; a rotor core that has; a cylindrical boss portion; a pair of yoke portions that are disposed so as to extend radially outward from two axial end edge portions of the boss portion; and claw-shaped magnetic pole portions that are disposed so as to extend axially from each of the pair of yoke portions and intermesh with each other; and a field coil that is mounted inside a field coil housing space that is surrounded by the boss portion, the yoke portions, and the claw-shaped magnetic pole portions.
Now, it is necessary to increase the cross-sectional area of the claw-shaped magnetic pole portions in order to pass sufficient magnetic flux to the claw-shaped magnetic pole portions. On the other hand, when the cross-sectional area of the claw-shaped magnetic pole portions is increased, areas of circumferential side surfaces of the claw-shaped magnetic pole portions are also increased. Areas of adjacent claw-shaped magnetic pole portions that face each other circumferentially thereby increase, increasing magnetic leakage flux. Thus, in order to maintain a balance between the two, the claw-shaped magnetic pole portions are made to have a tapered shape such that cross-sectional area is sequentially reduced from a base portion to a tip end portion (see Patent Literature 1, for example).
Patent Literature 1: Japanese Patent Laid-Open No. SHO 60-26444 (Gazette)